Accelerating SGMs. 
Recently there are various works proposed on accelerating diffusion sampling.
[1]}, [2]} used a dynamic programming algorithm
to find the optimal discrete time schedules to speed up the sampling of DDPM.
[3]}, [4]} utilized second-order numerical scheme to build a faster sampling process of DDPMs.
[5]} proposed DDIMs by using a non-Markovian diffusion processes to accelerate the sampling quality of DDPMs.
Later, DDIMs were further advanced by solving a differential equation on a manifold, so that the model can better approximate the ground-truth score functions [6]}.
[7]} distill a multi-step diffusion process into a single step via a student-teacher framework [8]}.
